Energy conversion device comprising a solid crystalline electrolyte and a solid reaction zone separator



Oct. 20, 1970 M. A. DZIECIUCH ETAL 3,535,163

ENERGY CONVERSION DEVICE COMPRISING A SOLID CRYSTALLINE ELECTROLYTE ANDA SOLID REACTION ZONE SEPARATOR Filed Nov. 21, 1966 6 Sheets-Sheet 1[III/ INVENTORJ A 7' TOR/V5 r5 3,535,163 ALLINE 1970 M. A. DZIECIUCH T LENERGY CONVERSION DEVICE COMPRISING A SOLID CRYST ELECTROLYTE Filed NOV.21, 1966 AND A SOLID REACTION ZONE SEPARATOR 6 Sheets-Sheet 2 no -W/10-(o) All/1415735 8 NQvQObQSQb Musk YWQ QSNR on Q wank m 2 W5 26 9 w M m ar a NM M M x 0 a w J. W

INVENTORY Oct. 20, 1970 M. A. DZIECIUCH ETAL 3,535,163

ENERGY CONVERSION DEVICE COMPRISING A SOLID CRYSTALLINE ELECTROLYTE ANDA SOLID REACTION ZONE SEPARATOR Filed NOV. 21, 1.966

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ENERGY CONVERSION DEVICE COMPRISING A SOLID CRYSTALLINE ELECTROLYTE ANDA SOLID REACTION ZONE SEPARATOR Filed Nov. 21, 1966 6 Sheets-Sheet 5X401) D/FF/MCT/ON POWDER PATTERN 0F CRVSHLL/NE .STQUCTURE FORMED FROM M206. W7. lo). M 692 /a)8 A1 0 (BALANCE) REL/1 T/ l/E INTENS/WOFD/FFRACTEDX-B4KS 26=AN6LE 0F DIFFRACT/ON xz AT may WAVE LENGTH OF A7908 FIG. I

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ATTORNEYS 3,535,163 ALLINE E SEPARATOR M. A. DZIECIUCH ETAL ENERGYCONVERSION DEVICE COMPRISING A SOLID CRYST ELECTROLYTE AND A SOLIDREACTION ZON Filed NOV. 21, 1966 6 Sheets-Sheet 6 X-PAY D/FFMCT/ONPOWDER PATTERN 0F SOD/UM BE T4 -/1L UM/NA 26' ANGLE OF D/FFRACT/ON X2ATX'RIYMVE LENGTH OF 7902 FIG. 9

MATTHEW A. DZ/EC/UCH NE/LL lag Z M ATTORNEYS United States Patent Oflice3,535,163 Patented Oct. 20, 1970 ENERGY CONVERSION DEVICE COMPRISING ASOLID CRYSTALLINE ELECTROLYTE AND A SOLID REACTION ZONE SEPARATORMatthew A. Dzieciuch, Dearborn Heights, and Neill Weber, Dearborn, Mich,assignors to Ford Motor Company, Dearborn, Mich., a corporation ofDelaware Continuation-impart of application Ser. No. 500,500,

Oct. 22, 1965. This application Nov. 21, 1966, Ser. No. 604,100

Int. Cl. H01m 11/00, 29/00, /00

US. Cl. 136-6 4 Claims ABSTRACT OF THE DISCLOSURE This application is acontinuation-in-part of our copending application, Ser. No. 500,500filed Oct. 22, 1965, now abandoned, the disclosures of which areincorporated herein by reference.

This invention relates to novel, cation-conductive, crystallinemulti-metal oxides, to objects formed therefrom, their preparation anduse. In particular, this invention relates to the use of thesecrystalline oxides as selective ion conductors. The important utilityfor these materials is their use as reaction zone separators and solidelectrolytes in electrochemical devices and processes, particularlythose for generating electrical energy.

The crystalline multi-metal oxides of this invention are useful in avariety of electrochemical cells as solid electrolytes which afiordselective cationic conduction between reaction zones and are, for allpractical purposes and to all practical degrees, impermeable to thereactants employed when the latter are in compound, elemental, oranionic state.

One such cell is a primary battery wherein electrochemically reactiveoxidants and reductants are separated by and in contact with a solidelectrolyte consisting essentially of a multi-metal oxide of thisinvention.

Another of these cells is a secondary battery wherein molten,electrochemically reversibly reactive, oxidants and reductants areseparated by and in contact with a solid electrolyte consistingessentially of a multi-metal oxide of this invention.

Another of these cells is a thermo-electric generator wherein a pressuredifferential is maintainedbetween anodic and cathodic reaction zonesand/ or between anode and cathode and a molten metal is converted toionic form, passed through a polycrystalline wall or inorganic membraneconsisting essentially of the multi-metal oxide of this invention andreconverted to elemental form.

Another of these cells is a thermally regenerated fuel cell utilizing asolid electrolyte consisting essentially of the multi-metal oxide ofthis invention.

Still another of these cells is an electrochemical device for separatinga liquid metal from a liquid salt thereof by electrofiltering such metalthrough a polycrystalline membrane consisting essentially of themulti-metal oxide of this invention.

The solid electrolyte half-cell separators of this invention consistessentially of a major proportion by weight of ions of aluminum andoxygen and a minor proportion by weight of metal ions having a valencenot greater than 2 in crystal lattice combination and cations whichmigrate in relation to said crystal lattice under influence of anelectric field, i.e. when a difference of electrical potential isprovided on opposite sides of said separator. In one preferredembodiment, the metal having a valence not greater than 2 is lithium. Inanother preferred embodiment, the metal having a valence not greaterthan 2 is magnesium. In another preferred embodiment, the ions of metalhaving a valence not greater than 2 are ions of both lithium andmagnesium. These separators when carefully prepared are essentiallyimpermeable to helium gas at 25 C.

The use of solid electrolytes in energy conversion devices for thegeneration of electrical energy is well known in the art. See, forexample, Galvanic Cells with Solid Electrolytes Involving Ionic andElectronic Conduction, C. Wagner, Department of Metallurgy,Massachusetts Institute of Technology, pp. 361377, in InternationalCommittee of Electrochemical Thermodynamics and Kinetics, Proceedings ofthe Seventh Meeting at Lindau 1955, Butterworth Scientific Publications,London, England, 1957, and Solid Electrolyte Fuel Cells, J. Weissbartand R. Ruka, Fuel Cells, G. J. Young, Editor, Reinhold PublishingCorporation, New York, N.Y., 1963. The solid electrolytes of thisinvention are characterized by high cationic conductivity and highresistance to physicalchemical attack by molten alkali metals and saltsthereof.

It is an object of this invention to provide an improvedcation-conductive reactant separator for cells employed to generateelectrical energy wherein at least one of the cell reactants comprisesan alkali metal.

It is another object of this invention to provide an improvement incells for generating electrical energy comprising a molten alkali metalanode, a cathode, an ionically-conductive cathodic reactant-electrolyteelectrochemically reversibly reactive with said alkali metal anode, incontact with said cathode and in ionic communication with said alkalimetal through a solid electrolyte by employing as such solid electrolytea crystalline, multimetal oxide having in combination a low electricalresistivity and a high resistance to molten alkali metal.

These and other objects and advantages will be apparent from thefollowing detailed description when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 illustrates the use of an ionically-conductive multi-metal oxideas a separator and solid electrolyte in a simple storage battery cellwith a liquid reactant-anode in contact with a first side of said solidelectrolyte and a cathode in contact with a liquid reactant-electrolytewhich 3 is in contact with said solid electrolyte on the side oppositesaid first side;

FIG. 2 illustrates the use of an ionically-conductive multi-metal oxidein a primary battery, i.e. a thermoelectric generator wherein heat isconverted to electrical energy utilizing a pressure differential betweenthe anodic and cathodic sides of the multi-metal oxide separator;

FIG. 3 illustrates the use of an ionically-conductive multi-metal oxidein another embodiment of a primary battery, i.e. a thermally regeneratedfuel cell;

FIG. 4 is a graphic illustration of the electrical resistivityproperties of a multi-metal oxide prepared in accordance with apreferred embodiment of this invention as a function of temperature;

FIG. illustrates a test cell with discharge and charge circuits employedto demonstrate change of cell resistance with time while employing amulti-metal crystalline oxide of this invention as a half-cellseparator;

FIG. 6 illustrates graphically changes in cell resistance with timeusing a multi-metal oxide of this invention and a control;

FIGS. 7 and 8 are photographs of recordings which translate into graphicform a defined portion of the X-ray diffraction powder pattern ofionically-conductive, multimetal oxides of this invention, said patternbeing characteristic of the preferred compositions of matter herein; and

FIG. 9 is a photograph of a recording which translates into a graphicform a defined (corresponding) portion EXAMPLE 1 Cylindrical pelletswere formed from oxides of aluminum, sodium and magnesium in accordancewith the following procedure:

(1) All starting materials were dried prior to use.

(2) In powdered form Na CO LiNO and A1 0 were added to a vessel andmechanically mixed for minutes. The A1 0 employed was in the form of0.05 micron particles (Linde B).

(3) The mix was heated at 1250 C. for one hour.

(4) The sample was mixed with a wax binder (Carbowax) and mechanicallypressed into pellets.

(5) The pellets were then isostatically pressed at 90,000

(6) The wax binder was removed by slowly heating the pellets to about550 C.

(7) The pellets were sintered in an electric furnace. During sintering,the pellets were kept in a covered crucible in the presence of packingpowder of the same composition as said mix or, in some instances, of NaO-A1 O (8) The pellets were weighed and physically measured.

(9) The electrical resistivities of the pellets were measured in thefollowing manner:

(a) The flat opposing surfaces of the sample to be measured were firstpainted with a saturated solution of silver iodide in ethylenediamine.The pellet was then heated to 400 C. to remove the ethylenediamine,leaving the silver iodide as a smooth adherent layer. The silver iodidewas then covered with silver paint to insure good electrical contact.The resistance was measured at 300 C. using 1.5 mc. alternating currentand the resistivity calculated.

The weight percent composition of Li O, Na O and A1 0 in these pelletsprior to sintering, the sintering time and temperature, the density ofthe sintered pellets and their specific resistivity are set forth in thefollowing table:

TABLE 1.-ELECTRICAL RESIgIIVIIIES OF POLYCRYSIALLINE MULTI-METAL OXIDESROM L120, N320 AND A1202 Sintering Specific Wt. percent individualconditions resistivity oxides used in preparation T1 T D L (ohm-cm meemp. ensi y 300 0. Batch identification No. L120 NazO A1203 (hours) C.)(g./cc.) 1.5 1110.

16 1, 440 2. 8G 7. 17 2 1, 460 3. 00 5 29 2 460 2. 95 0. 2 0. 99 9. J989. 02 3 1, 460 3. 00 4. 92 3 1, 460 3. ()2 5. 81 a 1, 400 3. 02 l 5. 103 1, 460 3. 00 1 3. 73 1(3 1, 440 2. 92 5. 32 g 1, 260 80 5. 11 1 4. 8398 88 17 1, 460 2.81 4. 90 1G 1, 480 2. 72 6. G4 2 1, 500 2. 76 7. 85

r 5 7. 32 84 64 2 1, 460 2. s9 14. 2e 2 1, 500 2. 41 43. 7 1G 1, 440 2.86 10. 53 0. 83 10. 00 89. 17 2 1, 460 2. 96 8. 60 12 1, 500 3. 05 4. 887 l 0. 66 10. 02 a9. 32 g 5 8 g: 18 1, 420 2. 80 6. 53 1g 1, :68 95 3.78 8 70 8. 09 1. 31 9. 96 88. 73 4 1 500 2 70 7 48 16 1, 520 2. 54 8. 592 1, 600 2. 56 11. 78 18 1, 420 2. 78 9. 19 1% 1,230 90 (i. (36

0 91 5. 1. 31 10.48 88. 21 4 500 72 7' 16 1, 520 2. 59 7. l2 2 1, 600 2.54 10. 83 1G 1, 440 2. 51 19. (i 3. 97 9. 71 8G. 32 2 1, 460 2. 81 37.81 g 1, 200 2. 46 31. 4 60 2. 8G 17. 2 0.16 10.08 89. 16 17 1 460 88 m 80. 33 10. 05 89. 02 3 1, 400 2. 84 12. 4 0. 49 10. 04 89. 47 3 1, 400 2.12. 7

1 After pellet had been immersed in sodium at 800 C. for one week.

EXAMPLE 2 N21 CO and A1 Data corresponding to that com- The procedure ofExample 1 was repeated except that p1led for the pellets of thepreceding examples is set forth MgO was substituted for L1 0 (from LiNOData corm Table TABLE 3.ELECTRICAL RESISTIVITIES OF POLYCRYSTALLINEMULTI-METAL OXIDES FROM L120, MgO, NAzO AND A120 Wt. percent individualoxides Sintering conditions Specific used in preparation resistivityTime Temp. Density (ohm-em.)

MgO Na O A120 (hours) C.) (g./cc.) 300 C. 1.5 cm.

15 1,520 2.92 8.6 1.32 9.95 88.41 10 1,520 2.80 11. 0 5 1,580 2. 05 13.416 1, 400 2.87 10. 2 3 1,520 2.84 13. 0 0.70 90.9 88.82 16 1,520 3. 07 55s 7 1,560 2.85 7.8 2 1, 000 2.06 13. 0 9.87 9.07 88.67 2.25 1,520 2.50I 10.0 17 1, 500 2.87 24. 5 1. 34 10.01 88.00 15.5 1,520 2. 74 e 57 171,520 2. 09 5 27 After being immersed in sodium at 800 C. for one week.

respondmg to that complied for the pellets of Example 1 EXAMPLE 4 1s setforth 1n Table 2. The procedure of Example 1 'Was repeated wlth the ad-TABLE 2.ELECTRIOAL RESISTIVITIES OF POLYCRYSTALLINE MULTI-METAL OXIDESFROM MgO, NagO AND A120;

Sintering Specific Wt. percent individual conditions resistivity oxidesused in preparation (ohmcm.), Time Temp. Den ity 300 C. MgO NazO A120(hours) C.) (g./cc.) 1.5 Inc.

17 1, 540 3. 08 3. 28 2. 5 9.0 88. 5 17 1, 580 3. 12 3. 97 17 1,580 3.16 4. 12 14 1,460 2. 7g 7 1, 500 2. 9 3. 92 9. 75 88. 33 3 1, 560 2. 9782 17 1, 580 2. 93 4. 98 17 1, 480 2. 89 18. 16 ,520 2. 94 5. 5. 00 9.75 85. 25 2 17 560 2. 91 6' 17 1,560 2. 86 13. 11 17 1, 480 2. 92 7. 4817 1, 520 2. 96 9. 36 3. O0 9. 75 87. 25 17 1,560 2. 81 14. 28 3 1, 6002. 89 9. l2 4 1, 625 2. 57 19. 49 16 1, 480, 1. 85 99. 19 13 1, 520 2.9. 52 7 560 2. 6. 72 00 75 25 4 1,600 2. 88 12. 51 16 1, 600 2. 83 4. 574 1, 625 2. 76 14. 36 17 1,480 2. 77 10.66 17 1, 520 3. 00 10. 65 2. 009. 75 88. 25 17 1, 560 2. 66 13.16 3 1,600 2.83 13. 42 4 1, 625 2. 4929.08 1528 3'33. 16 75 2 1, 500 2. 84 13.88 17 1, 560 2. 90 18. 85 16 1,480 1. 81 122. 36 3 1, 520 2. 63 19. 94 9. 00 9. 75 81. 25 17 1, 560 2.75 15. 81 16 1, 600 2. 58 17. 4 l, 625 2. 48 25. 17 4 1, 540 2. 69 37.04 11.0 9. 79. 25 4 1, 580 2. 84 21. 81 4 1, 625 2. 71 76. 32 16 1, 5502. 76 79. 00 13.00 9. 75 77. 25 4 1,600 2. 76 45. 2 2 i, 650 2. 68191.00 16 550 2. 52 201. 00 15. 00 9. 75 75. 25 l 4 1, 600 39 60. 3

EXAMPLE 3 dition of compositional analysis after sintering to ascertainThe procedure of the preceding examples was repeated the degree ofcorrelation between prefiring and post-firing except that both MgO andL1 0 (introduced as LiNO compositions. The results of these tests areset forth in were used in conjunction with Na O (introduced as a thefollowing table:

TABLE 4.COMPOSITIONAL CORRELATION OF CRYSTALLINE PRODUCTS WITH REAOTANICOMPOSITIONS 7 EXAMPLE Referring now to FIG. 1, a single cell secondarybattery is constructed of glass tubes 11 and 31, a slab 21 of acrystalline multi-metal oxide of this invention separating tubes 11 and31 and affixed thereto in liquid-tight relationship by glass seals 13and 33, and conductors 15, 17 and 19. The tubes 11 and 31 have aninternal diameter of about 12 mm. These and the glass seals 13 and 33are constructed of a glass having a coefficient of expansion close tothat of the slab, e.g. Corning 7052, Kovar. The tube 11 is partiallyfilled with molten sodium 15 and tube 31 is filled with a moltensodium-and-sulfur-containing reactant such as sodium pentasulfide (Na S35. The sodium and Na S are maintained in molten state by conventionalheating means not shown. The air in tubes 11 and 31 may be essentiallyevacuated and the tubes sealed or the cell may be operated in an inertatmosphere, e.g. argon. The slab 21 is about 12 mm. in diameter andabout 2 mm. thick with the face exposed to the reactants in each of thetubes 11 and 31 being about 1.13 cm. assuming a completely fiat surface.All other areas hereinafter recited are measured on this basis which maybe termed the geometric area.

In this cell the molten sodium serves both as the anodic reactant and asan electrode while the sodium-and-sulfurreactant serves both as thecathodic reactant and as a liquid electrolyte which is in contact withthe electrode 19. Ordinarily one would start the reaction with thecathodic reactant having a sodium to sulfur ratio of about 2:5 andterminate the cell discharge when this ratio is at least about 2:3. Acopper wire lead 17 extending into the sodium electrode 15 and astainless steel electrode 19 extending into the sodium pentasulfide 35illustrate ends of an external circuit, not further shown, which mayinclude a voltmeter, ammeter, etc. In the discharge halfcycle of thiscell, the sodium is attracted to the sulfur opposite the crystallinemembrane, gives up an electron, passes through the membrane as a sodiumion and combines with a sulfide ion formed at the cathode 19 withacceptance of an electron, thus causing an electric current to flowthrough the aforementioned external circuit. Recharging is effected byimpressing an external source of electric power upon the circuit with areverse electron flow in relation to that of the discharge half-cycle.

EXAMPLE 6 Referring now to FIG. 2 of the drawing, there is shown astainless steel vessel 101, e.g. about 1 inch in internal diameter and11 inches in length. Tube 101 has a flange 103 at its open end. Flange103 is provided with a groove or channel 105 in which rests a rubber Oring 107 which provides a vacuum-tight seal when the stainless steelcover plate 109 is secured to tube 101 by thread, bolt or otherconventional attaching means, not shown. Positioned inside tube 101 andaffixed to cover plate 109 is a smaller tube 111, e.g. about /2 inch ininternal diameter and 6 inches in length. The lower end of tube 111 isclosed by a circular plate 113 of a crystalline multi-metal oxide ofthis invention. The vacuum-tight glass seals 115 are provided to secureplate 113 to tube 111 and prevent passage of fluids between plate 113and tube 111. The lower edge of plate 113 is provided with a thinconducting layer of platinum brite paint 117, e.g. platinum chloride inan organic reducing agent, which in FIG. 2 is shown disproportionallythick in relation to the other components to facilitate its location andidentification. In practice this platinum layer is porous enough topermit sodium vapor to pass therethrough and sufficiently thick andcontinuous to conduct electricity.

Tube 101 is provided with an outlet conduit 119 having a valve 121. Avacuum pump, not shown, is connected to conduit 119 for reducing thepressure in tube 101.

Tube 101 is further provided with a heating element 123 and an outletconduit 125 with valve 127 for removing liquid from tube 101.

An inlet conduit 129 and valve 131 provide means for introducing aliquid into tube 111.

Tube 111 is partially filled with molten sodium 133. A copper wirenegative lead 135 to an external circuit, not shown, extends through aninsulator 137 and into the molten sodium 133. Insulator 137 extendsthrough cover 109. A copper wire positive lead 139 to the externalcircuit passes through an insulator 141 which extends through coverplate 109 and is in electrical connection with the film of platinum 117.In the alternative, lead 135 may be connected directly to tube 111 wheretube 111 is a good conductor.

In the operation of this cell, heat is converted directly to electricalenergy. Tube 101 is evacuated by pumping means through conduit 121 to apressure lower than about 0.1 mm. Hg and then sealed. Sodium 133 in tube111 is heated to a temperature of 300 C. or greater while the lower endof tube 101 is maintained at approximately 100 C. by the ambient roomtemperature. A difference in sodium vapor pressure on the two sides ofthe plate 113 results in the creation of a ditference of electricalpotential across the plate. As electrons flow through the externalcircuit, sodium 133 passes through plate 113 as sodium ions accepting anelectron from the platinum electrode 117 and returning to elementalstate.

Since the lower part of tube 101 is maintained at the relatively lowtemperature of about 100 C., the sodium condenses here and the pressurein the outer tube 101 becomes the vapor pressure of sodium at about 100C. modified by any pressure drop produced by the mass flow of sodiumvapor from the platinum 117 to the cooler walls of the outer tube 101.

One advantage of this thermo-electric generator is that the hot and coldparts can be separated to almost arbitrary distances thereby minimizingthe effects of wasted heat conduction between the hot and cold parts. Incontinuous operation, the condensed sodium in the bottom of tube 101 isheated and returned to the hot zone in tube 111.

EXAMPLE 7 Referring now to FIG. 3, there is shown in sectional view, avessel 201 containing molten tin 203. Extending into the molten tin 203is a smaller vessel 205, also shown in sectional view, with the lowerend closed with a plate, 207, a crystalline multi-metal oxide of thisinvention and a glass seal, not shown. In operation, vessels 201 and 205are closed at their upper ends and/or blanketed with an inert gas.Vessel 205 contains molten sodium 209. Conductor 211 is a negative leadto an external circuit, not further shown, and extends into the moltensodium while a positive lead, conductor 113, extends into the moltentin.

Vessel 201 is in fiuid communication with a decomposition chamber 219via an upper conduit 215 and a lower conduit 217. Decomposition chamber219 is in fluid communication with vessel 205 via overhead conduit 221and is provided with heating means, not shown.

This device converts heat into electrical energy. The sodium ions inplate 207 are attracted to the molten tin in vessel 201 and the contentsof this vessel are then represented by the formula NaSn Sodium 209releases electrons to lead 211 and the resultant sodium ions replace thesodium ions attracted from plate 207 to the tin 203. Such electrons arereturned via the external circuit and lead 213 to be accepted in theformation of NaSn in vessel 201. The reaction product NaSn passes viaconduit 217 to decomposition chamber 219 and is heated to decompositiontemperature. Sodium vapor passes overhead from decomposition chamber 219to vessel 205 via 9 conduit 221 while molten tin is returned to vessel201 via conduit 215.

EXAMPLE 8 Crystalline cylinders measuring about 1 cm. in length andabout 1.2 cm. in diameter were prepared in the following manner:

(1) Magnesium oxide is prepared by calcining basic magnesium carbonateat a temperature of about 816 C.

(2) The magnesium oxide is mixed with finely divided (Linde B) A1 as abenzene slurry.

(3) The benzene is removed by evaporation.

(4) The magnesium oxide-alumina mixture is then fired at about 1427 C.for about 30 minutes.

(5) The product of 4 is mixed with sodium carbonate as a benzene slurry.

(6) The benzene is removed by evaporation.

(7) The magnesium oxide-alumina-sodium carbonate mixture is then firedat about 1427 C. for about 30 minutes.

(8) The powder product of 7 the particles of which are less than about1, preferably not significantly greater than /3, micron, is then admixedwith a conventional wax lubricant (Carbowax) and pressed into cylindershydrostatically at 100,000 p.s.i.

(9) The wax lubricant is removed by heating the cylinders in air raisingthe temperature over a two-hour period to about 600 C. and maintainingsuch temperature for an additional hour.

(10) The cy inders are then sintered by packing the cylinders in MgOcrucibles with packing powder of the same composition, i.e. the powderproduct of 7, and heating at 1900 C. in air for minutes.

The composition of these cylinders is determined to be 6.3 weightpercent Na O, 2.18 weight percent MgO and 91.52 weight percent A1 0 Thecomposition is determined by conventional chemical analysis, i.e. sodiumby flame photometry, magnesium by titration using en'ochrome black T asthe indicator, and aluminum by difference.

Resistivity measurements as a function of temperature over a range fromroom temperature to 500 C. were made using one of these cylinders in anargon atmosphere. The results are illustrated graphically in FIG. 4 ofthe drawings. The weight of this cylinder was 3.16 grams.

Referring now to FIG. 5, a test cell was constructed using as the anodecontainer a glass tube 313 mounted in a heated well 311. A supply ofliquid sodium pentasulfide 315 is shown in the bottom of tube 313.Closing the upper end of tube 313 is a rubber stopper 317 through whichis inserted a smaller glass tube 319. The lower end of tube 319 issealed to and closed by a disc 321 cut from the cylinder tested forresistivity, FIG. 4. A supply of liquid sodium 323 is shown in thebottom of tube 319. A tungsten wire 325 is shown extending through thetop of tube 319 into the liquid sodium 323. The top of tube 319 issealed about wire 325. Also extending through stopper 317 is a Nichromeribbon electrode 327 which extends into the liquid sodium pentasulfide315 to a position immediately below disc 321 where it terminates in aloose coil.

Nichrome is an alloy containing about 58.5 weight percent Ni, about 22.5weight percent Fe, about 16 weight percent Cr and about 3 weight percentMn.

Electrically connected to wire 325 is a conductor 329. Ribbon electrode327 is electrically connected to a conductor 331. Electrically connectedwith conductor 331 is an ammeter 333. Between and in electricalconnection with conductors 329 and 331 is a voltmeter 335.

In electrical connection with the terminals 337 and 339 of conductors329 and 331, respectively, is a pivotable switch means 341. Switch 341can be periodically pivoted by timer 343 to place conductors 329 and 331into electrical connection with terminals 351 and 353 of a dischargecircuit 350 which includes conductor 355 and variable resistor 357thereby completing a cell circuit and initiating the discharge of thecell wherein sodium ions are transferred from inside tube 319 into theNa S in tube 313. Switch 341 may also be pivoted by timer 343 to placeconductors 329 and 331 in electrical connection with terminals 361 and363 of a charge circuit 360 comprising a conductor 365 and a batteryassembly 367 the power output of which can be varied. The latterconnection initiates a charging cycle whereby sodium from the chamberinitially containing Na S is passed through disc 321 into tube 319. Bycontrolling the electrical input, i.e. charge voltage, of the rechargingoperation and the load resistor during the discharge operation, the cellwas operated so that the difference between the charge drawn from thecell and the charge delivered to the cell was zero over a completecycle.

The open circuit potential of this cell measured 2 volts. The cell wasalternately charged and discharged at 30-minute intervals. Thecharge-discharge current was maintained at about 10 milliamperes.

Two such cells, hereinafter referred to as Cell A and Cell B, wereoperated with the anodic and cathodic reactants maintained at atemperature of 300i1 C. A control cell, hereinafter referred to as CellC, was operated with such reactants maintained at 296i1 C. The controlcell otherwise diflFered from Cells A and B only with respect to disc321 which was prepared in the following manner.

(1) A mixture of sodium carbonate and A1 0 in relative concentrationscorresponding to the eutectic mixture of beta-alumina and sodiumaluminate which melts at about 2900 F. was milled in a ball mill for 2days and then acid leached with dilute solution of HNO and HCl to removesodium aluminate and iron traces from milling. Beta-alumina isconventionally represented by the formula Na O-11Al O Sodium aluminateis conventionally represented by the formula Na O-Al O (2) A waxlubricant (Carbowax) was mixed with the powder and this mixture waspressed into cylinders hydrostatically at 100,000 p.s.i.

(3) The wax lubricant was removed by heating the cylinders in airraising the temperature over a two-hour period to 600 C. and maintainingsuch temperature for an additional hour.

(4) The pressed cylinders were fired at about 1816 C. in a carbon tubefurnace under an argon atmosphere. The cylinders were surrounded withcoarse particles (60 mesh) beta-alumina to prevent loss of soda. Thefired samples were chemically analyzed by the same methods disclosedearlier in this example and found to contain 5.75 weight percent Na Oand 94.25 weight percent A1 0 A cylindrical disc cut from one of thesecylinders with a diamond saw was used in the control cell.

The disc used in Cell C, the control cell, measured 2.8 mm. in thicknessand had a surface area exposed to the anodic reactant of 1.29 cm. Thecylindrical disc used in Cell A measured 3.28 mm. in thickness and had asurface area exposed to the anodic reactant of 1.16 cm. The cylindricaldisc used in Cell B measured 2.17 mm. in thickness and had a surfacearea exposed to the anodic reactant of 1.10 crnP.

As the crystalline disc 321 for the three test cells varies in exposurearea, the change of cell resistance data is brought into directcomparison through use of an A(RR factor in the following table whereinthe following legend is employed:

R=Cell resistance-ohms.

R =Initial cell resistance-ohms.

I=Time in days.

A=Surface area of ion-conducting disc 321 exposed to anodic reactant,cm.

TABLE 5.CELL RESISTANCE AND CHANGE OF SAME WITE TTME Cell A Cell B CellC t R A (Ii-Re) t R A (RR t R A (R -Rn) 7 6. 96 0 1 5. 70 0 0 8. 47 0 6.88 0975 2 5. 725 028 97 9. 29 +1. 06 12 6. 87 109 3 5. 66 044 1. 95 10.24 +2. 28 14 6. 84 147 6 5. 64 066 4. 68 12. 53 +5. 24 18 6. 85 133 8 5.62 088 5. 96 13. 80 +6. 88 21 6. 78 219 10 5. 63 077 7. 90 14. 51 +7. 7924 6. 83 158 14 5. 71 011 8. 75 15. 06 +8. 50 26 6. 91 061 17 5. 50 229. 89 15. 97 +9. 68 28 6. 86 121 5. 62 088 10. 81 16. 03 +9. 75 31 6. 94024 22 5. 66 4 11. 80 16. 52 +10. 38 33 6. 93 037 24 5. 65 055 12. 8516. 80 +10. 75 35 6. 97 012 27 5. 59 12 13. 95 17. +11. 84 39 6. 98 02414. 78 17. 67 +11. 87 45 7. 03 086 16. 05 17. 62 +11. 80 47 7. 09 15818. 18. 11 +12. 44 49 7.14 219 19. 18.12 +12. 45 52 7. 18 268 20. 17. 61+11. 79 54 7.21 305 21. 90 17. 96 +12. 24 56 7. 07 +.130 23. 0 17. 74+11. 96 59 7. 11 182 61 7. 20 293 63 7. 22 316 66 7. 31 426 68 7. 28 3897 7. 36 486 73 7. 40 535 12 The foregoing changes in total cellresistance in Cells A and C with time are illustrated graphically inFIG. 6 of the drawings.

EXAMPLE 9 Crystalline cylinders, about 1 x about 1.2 cm., were preparedin accordance with the first method set forth in Example 8, i.e. thepreparation of the TABLE 6.ELECTRICAL RESISTIVITIES OF NAzO-MgO-AlzOzCYLINDERS Wt. percent Electrical Wt. of batch eom- Cylinder resistivitycylinder Batch identification N0. pos1t10n No. (ohm-em.) gII'lS 1 3482.86 2 292 2. 79 3 220 2. 93 4 78 2. 78 Mg02. 33 42 126 Na207. 13 g P 1111201-00. 54 82 8 230 2. 91 9 275 2. 82 10 294 2. 90 11 256 2. 79 12296 2. 82

Average 289. 58

1 308 3. 0 2 320 2. 78 3 335 2. 98 MgO2. 02 4 340 3.02 123 Ni1z0-8. 14 5400 2 93 A120a89. 84 6 355 3. 0 7 325 2. 88 8 325 2. 88 9 310 3. 06

Average 335.62

1 378 3. O5 3 307 2. 99 M o-1. 72 124 812304.24 4 i 01 1 A 04 5 .122 3.05 a 0 340 a. 00 7 372 3. 01 8 352 3. 03

Average 368. 87

1 425 2 l1 MgO-2 s1 Naz08 13 g 2. g

Al O3-89 0s 4 540 J 2. 90 Average 511.25

1 MgO-3. 34 80 111.. Na2O10. 31 i Alz0386. 35 5 957 Average 930. 33

1 1 040 3 12 M 0-1. 51 I 119,. M304. 19 2 11020 A] O 30 3 340 3.12 2 3 41, 420 3.11

Average 1,080

1 3 020 3 02 Mg00 93 117 Na0-7 47 2 2.200 0 A] O 60 3 2, J00 3.01 2 3 4.100 2. 0

Average 2,555

MgO-2. 66 91-N Naz07. 38 1 264 2. 73

Mg02. 7s 1 232 3. 04 104 NazO-8. 81 2 340 3. 02 141203-88. 41 3 3. 12

Average 334 MgO-O 62 1 1,280 3. 04 118 Na2O 7 42 2 1,240 3. U5111203-91. 96 3 1. 210 3. 04

Average 1, 263

13 EXAMPLE gredients which measured immediately prior to sintering asfollows:

Weight percent llfla 7.93 g 3.44 A1 0 88.63

The cylinders were sintered at about 1850 C. for minutes. Representativecylinders were then subjected to chemical analysis and the sinteredcomposition was dcto sintering. This composition, the electricalresistance 10 termined to be as follows: and weight of the individualcylinders and sintering tem- Weight percent peratures for the respectivebatches are set forth in the Na O 7.71 following table: MgO 3.81 A1 089.42

TABLE 7.ELECTRICAL RESISTIVITIES 0F NaZO-MgO-AI O CYLINDERS Wt. percentElectrical Wt. of

batch Cylinder resistivity cylinder, sintering Batch identification No.composition No (ohm-cm.) gms. Temp., C.

1,720 85 liiSi'Si 3 333 333 1.720 ,850 A1203 90-55 5 2,370 2.88 1, 850 62,100 3. 01 1,850

g 2.76 1, 900 2.72 1, 000 89 g g 3 4, 300 2. 43 1,900 Al 3 4 3, 200 2.74 1, 900 2 3 5 2,200 2.32 1,900 0 2, 500 2.81 1, 900

1 34, 000 2. 34 1,700 90 i llg: 2 14, 000 2. 33 1,700 A1 49 3 22, 200 2.68 1,700 2 3 4 20,700 2. 32 1,700

EXAMPLE 11 Electrical resistivity (D.C.) measurements were madeCylinders Were P p in accordance with the first of these cylinders as inthe previous examples. These fell method set forth in Example 8 exceptthat NiO, ZnO, and C00 were employed in lieu of MgO and differentsintering temperatures were used.

The (D.C.) electrical resistance of each of these cylinders wasdetermined as in Example 5.

The composition of each batch of these materials was determined bychemical analysis after the last step prior to sintering. Thiscomposition, the electrical resistance and weight of the individualcylinders, and the sintering temperatures used for the respectivebatches are set forth in the following table:

TABLE 8.-ELEGTRICAL RESISTIVITIES OF NazO-NiO-AlzOa, Na2O-Zn0-A12O3, and

Wt. percent Electrical Wt. of

batch Cylinder resistivity cylinder, sintering Batch identification No.composition N o. (ohm-cm.) g'ms. Temp, C.

1 1 005 3 13 1 500 95-2 NiO-6. 66 i Na20s. 65 1 1, 070 2. 89 1, 900 113NiO-6. 3e 2 1, 700 2. 90 1, 000 A120534. 69 3 005 2. 93 1, 900

A12Oa 8544 2 2,350 3.02 1,800

C. The weights and electrical rcsistivities measured for these cylindersare set forth below. EXAMPLE 12 65 E was 1V1 y Cylinder N0; Wt., gms.(ohm-cm.)

3.03 463 Crystalline cylinders measurlng about 1 cm. in length 91 317and about 1.2 cm. in diameter were prepared in accord- :3; 33% ance withthe first method described in Example 8 ex- 3% :35 cept that therelative amounts of the ingredients were 1 510 changed as hereinafterset forth. Where sintering tem- 3:82 223 peratures were different thisis also indicated. 3% 52 5 Cylinders were prepared in such manner fromin- 15 Another group of cylinders were produced in like manner, diepressed at 4,000 p.s.i. and hydrostatically pressed at 110,000 p.s.i.Representative samples were analyzed with the following results Weightpercent Na O 7.77 M 0 3.81 A120 Remainder These cylinders were fired at1950 C. and tested for electrical resistivity (DC) as in the precedingexamples. The determinations made are set forth below.

Electrical Cylinder Resistivity (ohm-cm.) 1 470 The crystallinestructure of representative cylinders of aluminum oxide-sodiumoxide-magnesium oxide from Example 12 and the crystalline oxides ofExamples 1-4 were subjected to X-ray diffraction analysis and an X-raydiffraction powder pattern corresponding to the pattern graphicallyillustrated in FIG. 7 was repeatedly obtained.

The crystalline structure of representative cylinders of aluminumoxide-sodium oxide-magnesium oxide from Example 4 reveal an X-raydiffraction pattern that is quite different. This pattern is of the typeobtained from N320 11181203.

EXAMPLE 13 Plates of the trimetal oxides prepared in accordance with theprocedure of Example 8 of this invention are further used to produceelemental metal of exceedingly high purity from an ionizable compound ofthe metal sought to be recovered. In this use the plate serves as an ionfilter through which an impressed voltage and resultant current flowdrives the ion to be recovered as elemental metal.

Using a cell such as that shown in FIG. 1, a molten NaNO NaNO eutecticmixture at 245 C. is placed in the tube corresponding to 31 of FIG. 1.The plate or slab corresponding to 21 of FIG. 1 serves as theion-filtering device. A small amount of molten sodium is placed in thetube corresponding to 11 of FIG. 1 and a direct current from a directelectric current power source connected with the external circuit ispassed through the cell via leads corresponding to 17 and 19 of FIG. 1.The impressed potential is controlled so as to make lead 17 morenegative than the open circuit voltage of the cell. Sodium ions leavethe mixture, pass through the plate and elemental sodium is recovered.

EXAMPLE 14 An ionically-conductive multi-metal polycrystalline oxidehaving potassium ion substituted for sodium ion was prepared in thefollowing manner:

A mixture containing 9.75 weight percent Na O as Na CO 3.92 weightpercent MgO, and 86.33 weight percent Al O was shaken mechanically for30 minutes, heated at 1250 C. for one hour, mixed with wax, thenmechanically pressed into pellets. The pellets were isostaticallypressed at 90,000 p.s.i. after which the binder was removed by slowheating to 550 C. The pellets were then sintered in an electric furnace,i.e. heated at about 1550 C. "During sintering, the samples were kept ina covered crucible with Na O-Al O packing powder.

A sample pellet was placed in a clean crucible. This was placed open ona bed of dry K O-Al O in a larger crucible. The larger crucible wascovered and heated to 1380 C. for 64 hours to expose the sample to K 0vapor resulting from slow decomposition of the K O-Al O After cooling,the sample was washed in water and dried.

The electrical resistivity of the sample was measured by the method usedin Example 1 and its density was measured. This sample exhibited adensity of 2.92 and an electrical resistivity at 300 C. of 22.1 ohm-cm.

The electrodes used to measure resistivity were removed from the sampleand the sample was crushed and examined for composition. An X-raydiffraction pattern obtained using a cobalt tube (wave length about1.7902 A.) revealed that the compound was characterized by a peak at53.554.5 as opposed to the pattern which is obtained from Na O-1lAl Owhich is characterized by peaks at 52-53 and at 5556 and an absence of apeak at 54. Both compounds have several peaks in C0111- mon. The patternobtained for the sample duplicates the pattern obtained for thesodium-containing multi-metal oxides prepared in Examples 14.

Elemental analysis of the sample revealed that about 1.14 weight percentthereof was derived from Na O and about 11.80 weight percent from K 0.

Another of the pellets was placed in an open clean platinum crucible.This crucible was placed on a bed of dry KCl in a larger platinumcrucible. The larger crucible was covered and heated at 1100 C. for 3hours. This pellet was then placed in molten KNO at 400 C. for 16 hoursand then reheated in KCl vapor at 1100 C. for 3 hours. The sample waswashed with cold water and dried. The sample was tested in the samemanner as the preceding sample. This sample had a density of 2.75 and anelectrical resistivity at 300 C. of about 8.26 ohm-cm. Elementalanalysis of this sample revealed that about 0.66 weight percent thereofwas derived from Na O and about 12.76 weight percent from K 0.

Another of the pellets is converted to a lithium ionconducting ceramicby immersing the pellet overnight in liquid silver nitrate under anargon blanket and then immersing the resultant pellet overnight inliquid lithium chloride under an argon blanket.

For a discussion of conventional X-ray diffraction compositioncharacterization techniques, see Elements of X-Ray Diffraction" by B. D.Cullity, Addison-Wesley Publishing Co., Inc., Reading, Mass, 1956,Library of Congress Catalog No. 56-10137, particularly Chapter7Diffractometer Measurements. See also, An Introduction toCrystallography by F. C. Phillips, John Wiley & Sons, Inc., New York,NY.

It is to be understood that this invention is not limited to theexamples herein shown and described, but that changes and modificationsmay be made without departing from the spirit and scope of theinvention, as defined in the appended claims.

What is claimed is:

1. In an energy conversion device for the generation of electricalenergy electrochemically comprising an anodic reaction zone, an anode insaid anodic reaction zone, a cathodic reaction zone, a cathode in saidcathodic reaction zone, the improvement in combination therewithconsisting of a half-cell separator separating said anodic reaction zoneand the anodic reactions occurring therein from said cathodic reactionzone and the cathodic reactions occurring therein, said separatorcomprising a cationically-conductive crystalline structure, saidstructure consisting essentially of structural lattice and alkali metalcations which are mobile in relation to said lattice when a differenceof electrical potential is provided on opposite sides thereof, saidlattice consisting essentially of a major proportion by weight of ionsof aluminum and oxygen and a minor proportion by weight of ions of metalhaving a valence not greater than 2 in crystal lattice combination.

2. In an energy conversion device in accordance with claim 1, aseparator wherein said alkali metal is sodium and said metal having avalence not greater than 2 is selected from lithium and magnesium.

3. In a thermally regenerated battery comprising an anode container, amolten alkali metal within said anode 17 container, a cathode container,within said cathode container a cathode and a molten materialelectrochemically reactive with and thermally separable from said moltenalkali metal, conduction means electrically connecting said alkali metalin said anode zone with said cathode and forming a portion of anelectrical circuit, a regeneration unit spaced apart from said anodecontainer and said cathode container and comprising heating means andfluid separation unit, outlet means from said cathode container in fluidcommunication With said fluid separation unit, and inlet means to saidanode container in fluid communication with said fluid separation unit,the improvement in combination therewith consisting of a halfcellseparator separating said anodic reaction zone and the anodic reactionsoccurring therein from said cathodic reaction zone and the cathodicreactions occurring therein, said separator comprising acationically-conductive crystalline structure, said structure consistingessentially of structural lattice and cations of said alkali metal whichare mobile in relation to said lattice when a difference of electricalpotential is provided on opposite References Cited UNITED STATES PATENTS2,102,701 12/1937 Gyuris 13683.1 2,301,021 11/1942 Dalpayrat 136833,260,620 7/1966 Gruber 136-83 3,404,036 10/1968 Kummer et al. 1366WINSTON A. DOUGLAS, Primary Examiner A. SKAPARS, Assistant Examiner US.Cl. X.R. 136-83, 86, 153

